Particle beam radiation can be utilized in a number of different applications and accurately applying an appropriate amount of radiation can be very important. It is often critical to apply an accurate dose of particle beam radiation in medical therapy applications. Particle beam radiation therapy typically includes directing a beam of particles (e.g., ionizing particles, protons, etc.) at an area of tissue. The particles are usually associated with or include a charge. The particles are typically used to stop the growth or spread of the targeted tissue cells by killing them or degrading their cell division ability. While particle beam radiation is generally considered beneficial, there can be a number of potential side effects. The side effects can include unintended damage to DNA of healthy tissue cells. The effectiveness of particle beam radiation is primarily a function of the dose or amount of charged particles that is applied to cancerous cells while avoiding impacts to healthy cells. The amount of charged particles that are applied to the tissue is typically a function of a dose rate or “current” of charged particles and time the targeted tissue is exposed to the radiation. Faster dose rates usually enable shorter exposure times and that can have a number of benefits, including less opportunity for extraneous events to influence the therapy, increased productivity, and greater convenience to the patient.
Many conventional beam radiation therapy systems utilize ionization chambers (e.g., filled with air, a particular gas, etc.) to monitor the dose and dose rate of the particle beam (e.g., proton beam, electron gamma beam, etc.). The gas inside the ionization chamber is ionized by an externally generated particle beam while ions and electrons are collected by electrodes (e.g., by means of an external voltage applied to the ionization chamber, etc.). Typical drift times of electrons and ions are in the order of microseconds to milli-seconds respectively, and the gas amplification depends on the thickness of the gas layer. These drift times typically limit reaction times and detection tolerances, which in turn can pose problems as the dose rates increase. At high dose rates, recombination effects in the gas volume significantly suppress the signal and the chamber output is not proportional to or linear with the beam current. Thus, the ionization chamber usually can not provide a signal that is accurate and useful for monitoring high dose rates.
Conventional ionization chambers can also have problems with electronic noise in the monitoring devices. Electron charge collection can be influenced by magnetic stray fields and reduced air gap or short distances of beam monitoring components from the magnets. The magnetic stray fields can become a limiting factor in radiotherapy systems utilizing high magnetic fields (such as those using superconducting magnets, etc.). The particle beam (e.g., protons, electrons, etc.) can also be scattered by conventional monitoring components. In conventional ionization chambers a charged particle beam is usually widened due to multiple coulomb scattering when transiting the electrodes and the gas volume of an ionization chamber. Thus, traditional particle beam monitoring approaches can have a number of problems, especially as dose rates increase.